Plants have historically served many medicinal purposes. The World Health Organization (WHO) estimates that 4 billion people, 80% of the world's population, presently use herbal medicine for some aspect of primary health care. (WHO Fact sheet Fact sheet No 134, December 2008) However, it can be difficult to isolate the specific compound in a plant that has the desired medicinal effect and to reproduce it on a commercial scale. Additionally, while the active compound may be isolated from a plant, the other parts of a plant such as the minerals, vitamins, volatile oils, glycosides, alkaloids, bioflavanoids, and other substances may also be involved in the functioning of the active compound or the medicinal effect for which the plant is known, making the use, purification and commercialization of plant based pharmaceutical agents a challenge.
Phorbol is a natural, plant-derived organic compound of the tigliane family of diterpenes. It was first isolated in 1934 as a hydrolysis product of croton oil derived from the seeds of Croton tiglium, a leafy shrub of the Euphorbiaceae family that is native to Southeastern Asia. Various esters of phorbol have important biological properties including the reported ability to mimic diacylglycerols and activate protein kinase C (PKC); and to modulate downstream cell signaling pathways including the mitogen-activated protein kinase (MAPK) pathways. Phorbol esters are additionally thought to bind to chimaerins, the Ras activator RasGRP, and the vesicle-priming protein Munc-13 (Brose N, Rosenmund C., J Cell Sci; 115:4399-411 (2002)). Some phorbol esters also induce nuclear factor-kappa B (NF-κB). The most notable physiological property of phorbol esters is their reported capacity to act as tumor promoters. (Blumberg, 1988; Goel, G et al., Int, Journal of Toxicology 26, 279-288 (2007)).
12-O-tetradecanoylphorbol-13-acetate (TPA), also called phorbol-12-myristate-13-acetate (PMA), is a phorbol ester used in models of carcinogenesis as an inducer for differentiation and/or apoptosis in multiple cell lines and primary cells. TPA has also been reported to cause an increase in circulating white blood cells and neutrophils in patients whose bone marrow function has been depressed by chemotherapy (Han Z. T. et al. Proc. Natl. Acad. Sci. 95, 5363-5365 (1998)), and to inhibit an HIV-induced cytopathic effect on MT-4 cells. (Mekkawy S. et al., Phytochemistry 53, 47-464 (2000)). However, due to a variety of factors, including caustic reactions when contacted with the skin and concerns for its potential toxicity, TPA has not been shown to be an effective tool for treating, managing, or preventing disease. Indeed, as phorbol esters play a key role in activation of protein kinase C, which triggers various cellular responses resulting in inflammatory responses and tumor development (Goel et al., Int, Journal of Toxicology 26, 279-288 (2007)), phorbol esters would generally be excluded from possible treatment candidates for conditions that involve inflammatory reactions such as stroke.
Heart disease and stroke kill some 17 million people a year, causing almost one-third of all deaths globally. They are predicted to become the leading cause of both death and disability worldwide, with the number of fatalities projected to increase to over 20 million a year by 2020 and to 24 million a year by 2030. (Atlas of Heart Disease and Stroke, World Health Organization 2004).
While there are over 300 risk factors associated with coronary heart disease and stroke (Atlas of Heart Disease and Stroke, World Health Organization 2004), in developed countries, at least ⅓ of all cardiovascular disease is attributable to tobacco use, alcohol use, high blood pressure, high cholesterol and obesity.
Current treatments for the management and prevention of stroke are generally a combination of medications such as ACE inhibitors, aspirin, beta blockers and lipid lowering medications; devices such as pacemakers, implantable defibrillators, coronary stents, prosthetic valves and artificial hearts; and operations such as coronary artery bypass, balloon angioplasty, valve repair and replacement, heart transplants and artificial heart operations. “Increasingly, high-technology procedures are chosen over less expensive, but nevertheless effective, strategies” (Atlas of Heart Disease and Stroke, World Health Organization 2004) adding to the rising costs of health care and leading to marked disparities in the quality of treatment between different groups of individuals.
However, even where advanced technology and facilities are available. 60% of those who suffer a stroke die or become dependent and each stroke significantly increases the risk of further episodes. “Worldwide, treatment of cardiovascular diseases and their risk factors remains inadequate for most patients.” (Atlas of Heart Disease and Stroke, World Health Organization 2004). There is therefore clearly a need for new and more effective measures to treat and prevent strokes and to treat or prevent the long term effects caused by stroke.